Fire resistant wallboard



Patented Oct. 27, 1942 UNITED STATES PATENT OFFICE FIRE ansrsmn'rWALLBOARD Arthur 0. Salisbury, St. Helena, Oreg., assignor to Fir-TexInsulating Board Co., St. Helena, Oreg.

No Drawing. Application March 27, 1940,

Serial N0. 326,275 I 2 Claims.

consumer must be in keeping with the commercial requirements. Thefire-resistant wall board heretofore produced did not meet theserequirements. By the methods previously practiced in the making offire-resistant wall board, the inert material, for example, vermiculite,was either ground to a paste before being added to the pulp, or is afirst added to the pulp and the admixture then ground to a paste by aspecific refining process applied to the stock so produced. The board soproduced, however, cannot be made on the usual machine, such as afourdrinier. Vermiculite mixed with pulp and then reduced to a pasteproduces an excessively slow stock, because it tends to clog thedrainage-wires of the machine; and besides, by such admixture,'a largeportion of the vermiculite is carried away, and lost with the dilutionstill drained from the stock in forming the sheet on the wire of themachine.

Apparently it was heretofore believed that the fire-resistant quality ofa fibrous wallboard depended upon the micaceous,,or inert, componentbeing converted into a paste so that it would bedeposited on, andbetween the pulpfibers and coat the latter. But I found that such is notthe case; that an eflicient fire-resistant fibrous wallboard is obtainedif the inert material, i'or example, expanded vermiculite, be used'inthe form of granules of predetermined particle size admixed with anddisposed throughout the pulp stock. In my wall board the particles ofinert material constitute mechanical blocks between adjacent sections offiber, and function to intercept the transmission of sumcient heat froman ignited section capable of igniting an adjacent section. When mywallboard is subjected to intense heat the outer pulpfibers burn off,leaving the vermiculite particles exposed, which impose resistance tothe ignition of further fiber; the vermiculite particles also seal thevoids in the board against the entrance of air stimulating thecombustion of the interior fibers of the board,

The stock produced by my method will not clog the meshes of the machineon which the board is formed; and besides, practically all the inertgranules are retained in the stock during the 55 slstency of solids ofabout 1 /2 to 2% including draining ofl oi the dilution water on thewire. In short, I have discovered a commercially practical method,whereby a fire-resistant fibrous wallboard can be produced economicallyon the usual board-forming machines; and further discovered that theboard so produced has a fireresistant quality at least fully equal tothe board previously obtained by the old methods above described.

In order to produce my wall board, it is o! v course necessary that thegranules of expanded vermiculite, or other inert material, bedistributed throughout the thickness of the board produced. Expandedvermiculite granules will-float in water because having lesser densitythan water; but the granules will gradually absorb water, and in sodoing the density of the granules increases, and finally exceeds that ofwater, causing the individual granules to sink and become submerged atdiiferent levels, in accordance with their difierence in size; and thusthe vermiculite, component becomes stratified, as it were, at all levelsor horizontal planes in the sheet, while forming on the wire of themachine. I conceived that this characteristic of the micaceous granulescould be used to advantage in making a fire-resistant wall board. Inpracticing my invention the expanded vermiculite granules, or otherinert equivalent material, must not be introduced into the pulp stockuntil after all refining action on the pulp component has taken place;thus just ahead of the discharge of the admixture onto the wire of thesheet-forming machine.

Since the time within which said granules will absorb sufiicient waterand cause them to sink to different levels in the stock-diluting waterde-- pends upon the size of the granules, in order to obtain and assuredistribution of the granules throughout the thickness of the sheetproduced, I use only such granules of inert material as will be retainedon a 20-mesh screen. In other words, I found that efliclent distributionof the expanded vermiculite granules throughout the body of the sheetproduced, is assured by regulating the consistency of the stockdischarged on the wire of the forming machine.

The sheet of composition flowed onto the wire of the machine must have acertain degree oi fluidity in order to obtain the best condition forforming the sheet of wall board to be produced.

The granules of expanded vermiculite reduce the fluidity of thecomposition but very little. I have used successfully a mixture having aconlarger-size granules is that they would tend to float to the top ofthe sheet of composition while carried on the wire in the length of timethe composition must remain on the wire to effect its drainage ofsurplus water, and thus would concentrate the inert material in theupper stratum of the sheet, and correspondingly deprive its lowerstratum of the inert material, and prevent proper distribution thereofthroughout the sheet to assure the production of an emcientfire-resistant' wall board.

The objection to a smaller size of inert granules than such as retainedon a -mesh screen is that they would be lost with the water in whichheld in suspension and drained from the sheet of composition; and thewall board produced would lack the mechanical blocks intended toinsulate a burning or smoldering section of the wall board from adjacentsections,

It will be understood by all versed in the art to which my inventionrelates, that proper distribution of the expanded vermiculite granulesthroughout the thickness of the sheet produced is obtained by selectinggranules of proper particle size and by regulating the consistency ofthe stock discharged on the wire. While expanded vermiculite granulesfloat in water, because having a density less than water, the densitiesof the individual granules is changed by the amount of water they absorbwhile the stock is contained in the stock box; and thus when the stockis discharged on the wire of the board-forming machine, the granules ofexpanded vermiculite will be disposed at various levels in the sheetforming on the wire; and in that way be properly distributed throughoutthe thickness of the sheet of wall board produced.

Before the inert granules are mixed with the pulp stock, all refinementof the latter must be completed.

While the granules of expanded vermiculite vary in size, it is to beunderstood that the minimum and maximum sizes of the granules have beenselected approximately as above stated. The strands of fiberconstituting the web of my fiber board bind the components thereoffirmly together. The adjacent sections of fiber composing the body of mywall board are effectively insulated from each other by the granules ofexpanded vermiculite enmeshed in the web of the fiber. In other words,the embedding of the granules of expanded vermiculite in the fibercomposing the body of my wall board restricts the formation of the websof fiber encompassing the expanded vermiculite granules to such as incombustion will be capable of generating only a small amount of heat;and the insulation effect of'the granules of expanded vermiculite issuch as to confine the combustion of an ignited and smoldering sectionof my wall board, and prevent it from spreading by the transmission ofhigh temperature to and the ignition of adjacent sections.

The composition for making my wall board may consist of about 35 to 55parts by weight of wood pulp fiber, of the grade commonly used formaking wall board and commingled with water to produce a pulpconsistency, and about 65 to 45 parts by weight of expanded micaceousmaterial, specifically expanded vermiculite, dimensioned as mentioned.These ingredients must be commingled by gentle agitation to obtainthorough intermixture of the fiber and micaceous material.

The wide range in the proportions of micaceous material and fiber isbased upon the relative mechanical strength and fire-resistancerequirements in the wall board produced. Wall board having the maximumamount of micaceous material is intended for use only in places wheremechanical strength is not a factor.

I have found the employment of expanded micaceous granules of the sizementioned, as best for the making of my fire-resistant wall board.However, it may be'found that some other inert, porous material may besubstituted for expanded vermiculite.

But when substituting other porous inert material for expandedvermiculite then the quantity of the substituted material must bedetermined relatively to its specific gravity as compared with that ofexpanded vermiculite. And if this factor would require the use ofconsiderably larger amount of the substituted inertmaterial, the cost ofthe substituted inert material, or the increase in the weight of thewall board produced--and thus the increase in freight rates may notjustify the substitution.

I claim:

1. A method of making fibrous, fire-resistant wall board comprisingforming a stock of fiberpulp, completing all refinement of thefiber-pulp, intermixing with said fiber-pulp granules of an expandedvermiculite, said granules being selected in particle size within theapproximate range as will pass through a 6-mesh screen and be retainedon a 20-mesh screen, the resulting composite stock having a consistencysuitable for mat formation on the wire of a Fourdrinier machine,limiting the period of contact of the expanded vermiculite with thewater component of the stock so as to vary the densities of saiddifferent sized granules, then discharging on said wire the resultingstock, whereby said granules become disposed at various levels in themat carried by said wire and are distributed throughout the fibers ofthe mat, and finally forming a board from said mat.

2. A method of making fibrous, fire-resistant wall board comprisingforming a stock of fiberpulp, completing all refinement of thefiberpulp, intermixing with 35 to 55 parts of said fiber-pulp 65 to 45parts of granules of an expanded vermiculite, said granules varying inparticle size within the approximate range as-will pass through a 6meshscreen and be retained on a 20-mesh screen, the resulting compositestock having a consistency suitable for mat formation on the wire of aFourdrinier machine, limiting the period of contact of the expandedvermiculite with the water component of the stock so as to vary thedensities of said difierent sized granules, then discharging on saidwire the resulting stock, whereby said granules become disposed atvarious levels in the mat carried by said wire and are distributedthroughout the fibers of the mat, and finally forming a board from saidmat.

ARTHUR C. SALISBURY.

